1. Field of the Invention
The present invention relates to a field-effect transistor (FET) using a semiconductor, particularly to a high-withstand-voltage insulated-gate field-effect transistor (hereinafter referred to as power MISFET).
2. Description of the Related Art
An FET is a device in which regions called a source and a drain are provided in a semiconductor, each of the regions is connected to an electrode (a source electrode or a drain electrode), and a voltage is applied to the semiconductor via a gate electrode through an insulating film or a Schottky barrier so that the state of the semiconductor is controlled, whereby current flowing between the source electrode and the drain electrode is controlled. As the semiconductor, a Group 14 element such as silicon or germanium, a compound such as gallium arsenide, indium phosphide, gallium nitride, zinc sulfide, or cadmium telluride, or the like can be used.
In recent years, FETs in which an oxide such as zinc oxide or an indium-gallium-zinc-based oxide (also referred to as In—Ga—Zn-based oxide, IGZO) is used as a semiconductor have been reported (Patent Document 1 and Patent Document 2). FETs using such an oxide semiconductor have comparatively high mobility, and also these oxide semiconductor materials have a large band gap of 3 eV or more.